Osram MA/V Medium Pressure Mercury

This MA lamp represents the later style of production used by the GEC, which comprises very simple but highly effective arc tube mounts. A pair of steel wires have been formed into a spring arrangement which holds the arc tube centrally and offers superb cushioning against possible vibration or impact damage to the lamp.

The Osram lamp production was mechanised to a far greater degree than its competitors at Philips and Mazda and also overseas firms. MA arc tubes are traditionally sealed by glazing beaded molybdenum rods into each end of the tube, an operation which is carried out largely by skilled glassblowers. In the Osram process, the electrode wires were glazed and then pinch-sealed into each end of the open tube forming a very neat seal which required unskilled operators. The exhaust tubulation was affixed to the side of the arc tube body. This pinch-sealing technique not only lowered production costs, but it also allowed Osram to make use of cheaper drawn aluminosilicate tubing. To facilitate the hand-sealing operation, competitors generally employed expensive blown glass arc tubes, supplied dome sealed at one end and with a sharp constriction near the open end.

The glass used in this lamp is type H26X from the GEC's Lemington glassworks. This is a mid-range aluminosilicate which later became known as type A43 after GEC and BTH glass production was merged. Its intermediate softening temperature accounts for the luminous flux of this lamp being marginally lower than for Mazda lamps of the same era, whose arc tubes benefitted from the harder C46 (A431) glass. The outer bulb is made from X4 (S97) glass, also hand-blown at Lemington.